1. Field of the Invention
The present invention relates to a self-heating container using an exothermic reaction agent for heating a contained foodstuff in the form; of liquid or including a liquid substance without the supply of external thermal energy.
2. Description of the Prior Art
Various types of self-heating containers are known for heating the contents (mainly foodstuffs by heat of hydration between an exothermic reaction agent such as quicklime and water. One essential requirement in this kind of container is the capability of heating up the contents to a desired temperature with an easy operation and without any danger. Another important requirement is that the contents, particularly a foodstuff, be perfectly separated from the agent and never contaminated with the agent during storage and reaction. It is also important to ensure that the agent does not start reaction with the water until so desired.
A self-heating container that fulfills the above requirements is disclosed in U.S. Pat. No. 4,640,264 partly owned by the inventor herein. The container disclosed therein has been embodied and sold in Japan as containing Japanese sake and has become one of the most commercially successful self-heating containers. FIG. 1 schematically illustrates such a container which has a body 1 for containing a foodstuff 2 therein, the upper end of body 1 being closed by an upper cover 3. A can 4 is housed within the body 1 to confine a chamber 5 in which is arranged an exothermic reaction agent 6 together with a water bag 7. The lower end of can 4 has an outwardly extending flange curled to the lower edge of body 1, and the chamber 5 is closed by a partition 8 which rests on a lower cover 9 also curled to the lower edge of body 1. When it is desired to heat up the foodstuff 2, a sharp member such as a pin is used to rupture the bag 7 through the lower cover 9 and partition 8 whereby water is discharged to mix with the agent 6 for hydration.
The body 1 is made of composite material comprising a paper substrate and a synthetic resin layer coated thereon. The can 4 has to be heat conductive and is formed of metal material such as aluminum sheet, and the partition 8 is also formed of metal for resisting the hydration reaction and resultant heat. Further, in the container as actually sold the upper cover 3 is also of aluminum. It may be appreciated that use of these composite and metal materials substantially increase the manufacturing cost of the container. Additionally, the can 4 is formed by deep drawing of a metal sheet and is fixed to the body 1 by curling, involving difficult operations which also increase the manufacturing cost.
It is therefore an object of the present invention to provide a self-heating container which can be manufactured by simple operations and at low cost.
Another object of the invention is to provide a self-heating container in which heat generated by hydration may be efficiently transmitted to contents with minimum energy loss.
Still another object of the invention is to provide a self-heating container which can be stored or preserved for a long period of time without deterioration of an exothermic reaction agent.
A further object of the invention is to provide a self-heating container in which hydration may be effected by a simple operation.